The present invention relates generally to an internal combustion engine having a temperature rising device for increasing temperatures of related elements and, more particularly, to an internal combustion engine having a combustion heater.
For example, Japanese Patent Application Laid-Open Publication No. 62-75069 discloses a technology of enhancing a starting characteristic of the internal combustion engine and promoting a warm-up thereof in cold seasons by warming up engine cooling water utilizing combustion heat emitted from a combustion heater attached to a intake path of the internal combustion engine.
According to this Patent Application Laid-Open Publication, the combustion heater disclosed therein is attached to the intake path through a intake duct and an exhaust duct. Then, the air required for combustion is supplied from the intake path via the intake duct, and a burned gas is discharged to the intake path via the exhaust duct. The high-heat burned gas emitted from the combustion heater eventually arrives at the internal combustion engine body via the intake pass, and warms up the engine cooling water in a water jacket. Further, along the intake path, a switching valve for opening and closing the intake path is provided between a connecting point to the intake duct and a connecting point to the exhaust duct. This switching valve fully closes before the internal combustion engine is actuated, and, for a short while after the actuation thereof, half-closes (half-opens) or fully opens, thus controlling a quantity of combustion air supply to the combustion heater via the intake duct. This control is intended to promote the warm-up of the internal combustion engine and to enhance the starting characteristic thereof.
Incidentally, in the thus constructed prior art, it can be considered that a compressor of a supercharger is installed between the connecting point to the intake duct and the connecting point to the exhaust duct along the intake path. In this case, however, since the compressor hinders a flow of the intake air, there might be caused a pressure difference between on the upstream-side of the intake path and on the downstream-side thereof at the compressor serving as a boundary. Namely, a pressure on the upstream-side is larger than on the downstream-side. Thereupon, there might be produced a pressure difference between the intake duct connected upstream to the intake path and the exhaust duct connected downstream to the intake path. Then, an excessively large air flow occurs owing to the above pressure difference within the body of the combustion heater connected to the intake path via the intake duct, and the exhaust duct, and hence there might be a possibility in which therefore an ignition characteristic of the combustion heater declines. That is, in the same way as a gas lighter and a match are hard to gain a fire when it's a strong wind, the combustion heater is hard to gain a fire when a velocity of the air flowing within the combustion heater body is high, or if the fire is set, it can be considered that the fire is easily extinguished.
Further, in the case where the compressor is, as in the way described above, attached to the intake path between the connecting point to the intake duct and the connecting point to the exhaust duct along the intake path, when the compressor is operated, a pressure in the vicinity of the compressor on the downstream-side at the compressor serving as the boundary along the intake path, i.e., the pressure on the side of the connecting point between the intake path and the exhaust duct becomes higher due to pressurization than a pressure in the vicinity of the compressor on the upstream-side at the compressor similarly serving as the boundary, i.e., the pressure on the side of the connecting point between the intake path and the intake duct. Therefore, it follows that there is produced a back flow in which the intake air flows back to the intake duct from the exhaust duct also within the combustion heater body connected to the intake path via the intake duct and the exhaust duct. If this back flow is produced, a so-called back fire phenomenon occurs. The back fire phenomenon means that a fire of the combustion heater is directed backward to the intake duct. There might be a possibility in which an accidental fire is caused in the combustion heater, and it can be considered that the internal combustion engine is incapable of obtaining a sufficient quantity of heat from the combustion heater.